a) Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to technique for forming a blanket tungsten film for inter-layer connection of laminated wiring.
b) Description of the Related Art
Normally, as a plug for connecting wiring layers of multiple layer wiring, tungsten W which is a refractory metal has been employed. However, tungsten has a weak adhesion with SiO.sub.2. Thus, For forming a W film on an inter-layer insulating Film formed of SiO.sub.2 (including doped oxide), laminated adhesion layer of titanium (Ti) Film/(titanium nitride (TiN) film, TiW film, or WSi Film) is formed first and then W film is formed thereon.
For forming a W film, normally for improving growth rate of tungsten and uniformity of its surface, a substrate is first subjected to flow of silane (SiH.sub.4) or dichlorosilane (SiH.sub.2 Cl.sub.2) For forming a thin film of silicon. Thereafter, gas flows of SiH.sub.4 or SiH.sub.2 Cl.sub.2, and tungsten hexafluoride (WF.sub.6) are supplied on the surface thereof for tungsten-silicidizing the thin film of silicon and form a tungsten silicide (WSi) film. Then, gases of hydrogen (H.sub.2) and WF.sub.6 are allowed to flow over the surface. WF.sub.6 is reduced by H.sub.2 and a W film is formed on nuclei of WSi.
Here, the method described above has an effect of preventing direct reaction of Ti and WF.sub.6 when an adhesion layer is a Laminated layer of Ti/TiN films and a W film is formed on the adhesion layer. A direct reaction of Ti and WF.sub.6 will form a solid substrate which will exhibit a volume expansion and become a cause of peeling-off of a layer.
When an adhesion layer for forming a W film is formed by sputtering, the substrate is often fixed on a mount using a holder or hooks. At portions under these hooks, an SiO.sub.2 film which is an inter-layer insulating layer is exposed because almost no film is formed under the hooks by sputtering. When a W film grows on the exposed SiO.sub.2, the W film is easily peeled off because of weak adhesion anti particles are produced.
To prevent a growth of W film on the exposed SiO.sub.2 film, the exposed SiO.sub.2 film around the substrate is covered with a ring for preventing reaction gas from reaching the exposed film of SiO.sub.2.
In the prior art method of forming a W film described above, when a gas of SiH.sub.4 or SiH.sub.2 Cl.sub.2 is allowed to flow on a surface of a substrate for forming thereon a thin film of silicon, it is not supplied on the portion covered by a ring for preventing penetration of reaction gas. Thus, a layer of SiO.sub.2 is exposed on a periphery of the substrate.
In the next process of forming WSi film by providing a flow of WF.sub.6 gas, WF.sub.6 may penetrate into a portion where SiO.sub.2 film is exposed on a periphery of the substrate. In this case, a W film grows directly on the SiO.sub.2 film, and results in a production of particles.